Pyrometric device



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WWBMMM ATTORNEYS Y, Patented N0v.4,`19411 PYRDMETRIC DEVICE;

, Luis lde" Florez, Pomfret, Conn.; and Emmen Bach, 'i' Y .".Yonkers, N. Y.

' Application June 14, 1938, Serial 1510.213594 1ol Claims. j(c1.'236 14) 4This invention vrelatesto devices for controllingY temperature, and more'particularly to' apparatus for maintaining the temperature in a `given temperature zone at a constant value by adjusting `the temperature in a second related temperature zone.

` *Temperature control of the outlet temperaturef a tubular oil still, can usually be traced to one of two main fcauses.,- .The rst of-these'is the change in the v temperature of the furnace which produces heatV forvthe distillingor cracking process, such as might result from a change in the' caloric value "precederchanges in the; outlet temperatureby a '21 lag andheat transfer characteristics of the systhe outletjtemperature occurs.,V

A second frequent cause forkchange is that the l outlet temperature of the still may also vary with fthe operating load, in which case changes inthe 4furnace temperatureJn order tovrestore the outletrtemperatureto the desired value, mustbe very Y -carefullyamade since the hugemass of brick and "steel o'f'whichV the furnace is constructed vmust Y sulting therefrom.

*induce an undesirable .cyclic swinging, or-hunt' of the fuel used. Changes Y of this character l :"control temperature will occurgeven.tljioughthe t rtemperature of vvthe furnace 'remains vat aAv conkstant value.` In thisr case the adjustment ofthe disturbances in vindustrial processes, such as are experienced for example/in the :trolvternperature are the result of-factors otherV Y. given periodof time, 'depending on the thermal i changes in the temperature of a related temperi ature zone.

Another object Vof ,the invention istoprovidef an apparatus of the above character whichl is adapted to fcorrect changes in the temperature of the related temperature zone beforeijany f change in the control temperature; hasgtaken A- furtherobject ofthe inventionis .to provide an apparatus of the above character which is adapted to adjust the temperature of ltherelated temperature zone in order to maintainja-constant control temperature,r Where. changes in theY conthan changes in the related temperature zone. Y In a preferred embodiment ofthe invention, an electrical temperature responsive f element is ,placed in the zonewhose tempeaturefit is dey tem, and 'if notedA in time, can be corrected byv vadjusting thefuel 'supply before anychange in be very slowly heated or.v cooled in order to preventunequal expansion' and possible ldamagere- Y* 1 sired to control, andaV second elementV responsive tothe rate of change ofl'ftemperaturejis-placed Yat some selected point in a relatedtemperature zone in which changes` in temperature-occurfin Q advance of those, at the control point. Botnial temperature responsive element andthe rate vof change responsive element are connected infse- Y ries and the outletofjtheV seriescircuit islmade to actuatea controller of anwell'known type which Y supplies',V air '-under Ypressure toga fuel valveV and thus governs the amount of fuel supplied to af heating element in the related temperature zone.

The rate of change responsive element fmay l consist of a pair 'of substantially identical elec-V trical temperature responsive devices whichfare net eiect ofthe two'in series" is zero.v vQnejoi Y these devices may be directlyexposed toftheheatj Y at the related temperature'-izone,V andthe otherrk I I f*irikcaffasV itis called, of theternperatureabout the f1 control setting, dueto. the time lag *existing be'-VV 1 temperature. i Y fDevices of the Atr'rev .fuel change` to the net'effe'ct of both the tween fuely changeV and changes of the control'v character* disclosed in priorA Patents Nos. 1,837,853 and"2,r054,120 proportion-` change in temperature andthe rate at which'the change( takes place, so that fby theiruse, dis' ely corrected without hunting Schange in thecaloriiicvalueof the fuel until 'j the latter change is reflected as a changeinfthe l outlet temperature. y i

4@The principal-object of theprescritfVVtDliOi accordingly, "is to .-providevan apparatus ierlanf Y' ticipating changes in the contro-l temperature'be-V Vfore they occur, in a system `where changes in Y the control tcrnperaturefmaybe precededfby i' ..-tu r bancesin 'the outlet temperature can'be qu'ick-Y 'I With all of ythese devices, however, o' regula- Y 's tory action lcan be initiated to compensate for aY i maybe. lagged Yin the manner disclosed'iri A our mediately respon'd'to changes in the temperature of thejrrelated zone. jThusijfor algiven'iclfiange in the Ytemperature of the related temperature 1' .,zone, one device'of thefrate ofv change element l Y -wi1l `respond* directly, andtheV otherl will@ respondV 1- ymore slowly, dependingjron the'heattransferV characteristics ofthe lagging materi-a1'used.` AUrl-1 derV these conditions, a temperature 'Kdierence Y Aexists between the'two'devicesand the re'sultingl E; M. F( isof a magnitude-andsign correspond-y Vingf'to the rate andldirectlonof temperature l Y Y change of the zone in which the rate 'respony sive element. is immersed.' If Ynow-no further f change in:temperatureoccurs,lthel laggeddevlce Vwill increase its response until-it too'hasV reached the normal steady state Vtemperature of its sur-l` roundings. lNew `'withbothdevices of therateVirr ofchange responsive element at'the Vsame 'tempcrature the net effect Vis'agaln zero.

YThe operation of thisnovel tempera-turesre-fif sponsive apparatus may be better understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Figure 1 is a schematic diagram of a temperature control apparatus constructed in accordance with this invention;

Figure 2 is a schematic diagram similar to Figure 1 in which a plurality of rate of changev re sponsive elements are used to amplify the rate of change response;

Figure 3 is a schematic diagram illustrating a modified means for amplifying the rate of change response;

A,Figure 4 is a schematic diagram of a modification of the invention in which resistance thermometers are used in place of thermocouples; and

Figure 5 is a schematic diagram of a further modification of the embodiment of the invention shown in Figure 4.

Referring to Figure l, an element responsive to the control temperature is shown at 9 and it comprises a thermocouple formed of two dissimilar metals, such as for example a Wire of constantan J and a wire of iron I I which are joined together at one end to form a hot junction I2. It will be obvious that numerous combinations of dissimilar materials may be used, and the inven-- tion is'not intended to be limited to the specific examples shown. Connected in series with the control temperature responsive element 9 is an element I3, responsive to the rate of change of temperature in a second temperature zone related to the control temperature, and in which changes of temperature may precede those at the control point.

The rate of change responsive element may comprise a pair of oppositely connected thermo? couples formed from the dissimilar Wires I4, I and I6, Whose extremities are joined to form the hot junctions I1 and ,I8, Thus'the wire I4 and the Wire I5 up to the portion I5 form one couple having the hot junction I1. The remainder of the wire I5 beyond the portion I5' together with the wire I6 forms a second couple having the hot junction I8 which is connected in series with the iirst couple in such fashion that their E. M. .Fs are opposed. The wires I4. and I6 may be of chromel and Wire I5 may be of constantan, although obviously other combinations may be used, provided only that wires I4 and I6 are of the same metal. The junction II is provided with lagging IS such as is disclosed'in our prior Patent No. 2,054,120, and which may be a large mass of metal or any other suitable lagging material.

The rate responsive element is connected through the wires I4 and I5, respectively, with wires and 2l, which may be of copper, in series with' the control temperature responsive element. These connections form a number of junctions 22, 23 and 24, 25, which are enclosed in the junction boxes 26 and 21, respectively, in order to maintain the respective sets of junctions at the same temperature so that they will not introduce extraneous E. M, Fs into the system.

The open end of the series circuit is connected to a controller 28 at which point the cold junction (not shown) may be located. This controller is of a well known type, in which the E. M. F.

Vfrom the thermocouple circuit may be used to .control the passage of air to a fuel valve 29, but

the form of controller is no part of the present invention. The fucl valve 29 is provided with a 29, whose movement is balanced by the after pressure of the fuel in the feed pipe 3|, which is connected to the underside ofthe exible member 29' through a pipe 32. The pipe 32 is connected to the pipe 3l at a point in the Vfeed line suiciently removed from the valve to minimize error due to turbulence caused by the passage of the uid through the valve in the direction shown by the arrow.

Since under static conditions the E. M. Fs of the two opposed couples are equal and oppositely directed, the controller 28 need be calibrated for the control temperature couple 9 only, and the metals used in the rate of change responsive element I3 may obviously be different from those in Y the couple 9 if desired.

In a specific application of the temperature controlling apparatus, the hot junction I2 of the control temperature responsive element 9 may be placed in a zone whose temperature it is desired to control, such as for example, the oil stream at the outlet of a tubular oil still, and the hot junctions I1 and I8 of the rate responsive element I3 may be placed at a selected point in a related temperature zone, such, as, for example, the furnace which provides heat for the distilling coils in the still. As has been mentioned above, a definite time lag exists between temperature changes in the furnace and temperature changes at the outlet, which depends on the heat transfer characteristics of the system. In accordance with the presentinvention, the lagging I9 may be so designed that the lag in the temperature of the hot junction I1 with respect to the hot junction I8, is essentially the same as the lag between the control temperature as measured by the control temperature responsive element 9. and the furnace temperature at the rate of change responsive element I3.

Assuming now that steady state conditions exist, an E. M. F. exists at the junction I2 which is directed as indicated by the arrow, and similar E. M *Fs exist at the junctions I1 and I8, respectively, which are directed as indicated by the arrows shown in Figure 1. It will be noted that the E. M. Fs at the junctions I1 and I8 are opposite in sense, and since the two couples of which these junctions are a part are made of the same metals, for a given steady state hot junction temperature, these E. M. Fs are equal in magnitude, so that the total response is zero. It will also be observed that the direction of the E. M. F. at the junction I2 is the same as that of the E. M. F. at the junction I8, but is opposite in direction to the E. M. F. at the junction I1. Thus, the net impulse, or electrical effect, of all junctions is the algebraic sum of the impulse due to deviation of the control temperature and that; due to the rate of temperature change of the related temperaturezone.

Let us assume now that due to a change in the caloric value of the fuel supplied to the furnace through the pipe 3|, the furnace temperature increases. This temperature increase will be directly followed by the junction I8, but will not be instantaneously followed by the junction I1 due to the lagging I9 in which it. is embedded. There will therefore be a resultant E. M. F. in the circuit which will be directed as shown by the arrow at the junction It` and which will actuate the controller ,'28, decreasing thc air pressure above the flexible member 29' and thus retemperature is restored., n ,f

l In the modification showninFigure 2, the, rate of ychange responsive device consists of a plurality :of unlaggedhot junctions. I8 and an'equal number of` junctions II1 which Vare provided with lagging kmaterial 59, fand* all of which are confurnace is instantaneously corrected before it can affect the temperature oftheoil` at the outlet, which Vis-measured by the "control temperature i I responsive element 9. i

f Myers-0f l this character win give Aincorrect- ,n- M.y F.- va1ues, it isimportant that thisprecautionbeobservedfI f i .If-now, due perhaps tov a change in load,-the f f* controltemperatureat the outlet'of `the'still decreases, theE. M. F. of the control temperature 'responsive element 9 will drop, thusl actuating the controller 28-and increasing the pressure of the airsupplied above the` flexible member 28 of the hot junction I8 of the rateof change responsivefelement` I3 increases accordingly. The

direction frof the arrow at the junction I8.VA Y It will ber noted thatthe direction ofthis rate of 'change E. is in the same direction'as the E. M. F. generated at the vcontrolftemperature responsive'elernent'f! at the stillA outlet.` `By f a`suitab1e choice ofv thermocouplezwires, the `lncrease in E. M'. F.from 'the rateof change responsive device may be made exactly equal to theV decrease in the E. iM.;F. of the control tempera.- ture responsive device, so that thetotal E. M. F. Ain thercircuit is restored tothe normal. value.

Meanv'vhile, the temperature of the lagged junction I1/ slowlyV increas'eaand sinceits time of'- lag has been vchoseny to be Vthe same ,asfA the time of lagl in ytheV fsystem, the' temperature of t the-junction I1 jincreases'substantially indirect proportion to the increas'ein temperature at vthe outlet."y Under these conditions; the net impulse vfrom the rate responsive elementt'endstol cancel the impulse'due to the drop'ln outlet; tempera-vv ture, and the-controller is restrained vfrom effect-A VVVing too rapid a change4 in fuel. f

It will beL evident. therefore, thatwith the tem- -v f perature control .apparatus of this invention,

changes in fuel value are immediately compenv sated vfor and the fuelsupplyto the 'furnace adjusted before any vchange in the outlet temperature occurs. Thus, it is now possible to maintain the outlet temperature constant and independent of vvariations in the` caloriilc value' of the fuel.

Furthermore'where changesv in the outlet temperaturel occur due to changes in theA load, the furnace temperature may be adjusted ata/.rate vwithin its safe. limitsl until the desired outlet nected in. series to provide la' rate .of chang E.'M. F Iof large magnitude.

Y v The same result may be obtained as shown in Y If f desired, temperature responsive elements x otherthan thermocouples may be used, as is in# :.dicated in. themodiication shown? in Figure 4, in which resistance elements are;used.in con'- junction-with a resistance: bridge as therate of change'responsiveelement. In this modification,

kand openlngthe fuel valve to increase the sup- 1 plyof fuel fed to the furnace. vAs a result ofthe increasein fuel supplied, thel temperature of the furnace begins to increase andr the ktemperature as in the '.others, .the thermocouple Sis-'located in vthe temperature zone to be controlled, such` as in the outlet of anoil still. -Ata selectedl point in the furnace, a pairof substantiallyelectrically identical resistance elements 38. and 3 9: are in serted. the element 38 `being providedwlthflagyging 40 which is similar in charatentothealag; ging laprovidedfor the junction I;1.;f The elements 38 and38 are connected .at oneendto a f be kept atA theA vSame temperature".y in order tocommon point 4I which forms one of thevertices lof= a resistance bridge, andat the other end to Y the wires 42 and43, respectively, forming` the junctions 44 and45, respectively. Thefcommon pointl .4I is also connected kto a lwire- 4Iiforming- Ythe junction 41. f

-The junctions, 45, and ansuitable junction box 48 in which they; may

- prevent thermoelectric E. F's from acting in .the bridgeeircuit.v The wires 42 and 43- are -connected toa resistance bridgewhich -isformed by resistors 48,138, 39 andllfinfonegarmand resistors 5I and 52 in the other. Thecommon point o f the resistors l43` and 5I, isv connected through a wire 53, a variablenesistor54 and, a j

source of, voltage 55 to the common point of .the resistors 5 0 and 52.

the `control temperature kresponsive element 8 is broken and is connected at the junction 51 through a wirev56 to the common point of Vthe L resistors 5IV and 52. The wire 4,6 is connected tothe other end of the wire II forming a. june--V -tion 58, sothat the voltage between the common point of the resistors 5I and 52 and thexpointfr l 4I `is connected in series with the M, of the control Atemperature responsive element, 9. -In operation, and assuming thatsteady state j conditions exist, the rresistanceelements'38 andv 38 are at thesame temperature andtherefore .Under lthese 1 conditions,` the resistance bridgeis balanced and have kthe `same resistance value.

Uno voltage exists between the point 4I and the common point of the resistors 5I andy 52,-" If,V I

Y however, the furnace temperature now increases,

Figurel 3 by inserting an amplier 33 inthe cir-" shown in Figure 1. -Obviously,-by adjustingthe gain of amplifier 33,the impulse of the rate of change responsive element mayjbe given any desired value." Thcijunctions 34, 35 and'36, 31, re-

. .spectivelv should be kept at the same tempera- 'i ture in orderjto prevent extraneous E'.y M.'F.'s from appearing in the circuit. Since extraneous V`cuitl of the' rate of change responsiveelement the unlagged element 39 will also increase in'.- temperature and its resistance value `will .in-

crease accordingly. The velement 3 8 being lagged. y.

however, will not respond instantaneouslyto 'the change'in vtemperature lso v that its resistance A. value will remain essentially 'unchangedj. A Thisj4 change 'in resistance" will unbalance: the bridge and avoltagewill exist across the common point of the resistors 5I and 52 and the'point 4Iw'hich kacts in the same direction-'asthei E. M, F. at` the junction I2 of the control temperature responsive element 8. Thisjincrease in the F.

in the. circuit will acttofdecrease"thefuelsup plied tothe furnace insthe mannerd'escribed vabove, thus reducing the-furnace temperature to the normal value. 'The resistance element 39 VY therefore plays the same part as the thermocouhot junction I8 shown ple which includes the inFigures .-1, 2 and 3.

41 are enclosed Vin Byk means-'of resistor 54 the voltage applied'across the-bridge may bev adjusted to give 'the rate of change of temperature impulse any desired value. The wire .I i of In the case where the control temperature decreases, for example, due to a change in load, the controller will again be actuated as described above to increase the supply of fuel to the furnace. The increased fuel supply will cause the furnace temperature to rise, thus again changing the resistance of the element 39 and inserting an E. M. F. in the control circuit which will substantially balance the decrease in the E. M. F. at the junction I2 due to the drop in temperature. i

As in the case of thefcouple I1, the lagging 48 isso designed that theV time of lagy between the element 39 yand the element 38 is substantially' the same as the time of llag betweenthe control temperature and the furnace temperature. Hence, as the temperature of the element 38'slow'ly increases, its resistance value will also increase, thus restoring the resistance bridge to its normal balanced condition. If the outlet temperature measured bythe junction l2 increases substantially at the same rate as the position and no further change in fuel will be made.

v inlet Vand the outlet, of the distilling and cracking coil to anticipate changes in outlet temperature resulting from changes in inlet temperay ture. It is to be understood that all such modifitemperature of the element I8 isincreasing, the v total E. M. F. in the circuit remains essentially constant and no further change in fuel supply is made. v

The same results ,Y may be accomplished by means of the apparatus shown in Figure 5 in which the resistance elementsl 38 and 39 in the resistance bridgeVV are' replaced by4 a slide wire resistance 68, which isconnected at one extremity through the wire 42 to the resistor 48 and at the other extremity through the wire 43 to the resistor Il. The wire 46 is connected to a contact member 6| which moves on a lead screw 62, by means of which its point of contact with the slide wire 60 may be adjusted. The lead screw 82 is driven through the gearing 63 by a controller 64 which may be, for example, the automatic recording mechanism usually associated with temperature recording equipment, and which is actuated by means of a thermocouple 65 located in the related temperature zone. V

In this modification a change in the temperature of the related temperature zone gives rise to a thermoelectric impulse in the thermocouple 65 which actuates the controller E4. 'The controller 64 drives the lead screw B2 through the gearing 63, thus moving the contact 6l from its normal balanced position on the slide wire 50 to a new position which unbalances the resistance bridge. The movement of the contact 6l is transmitted through the springs 66 to a slide' member 61 to which the slide wire 60 is fr secured. Secured to the lower end of the slide 61 is .the shaft 88 of a dash pot 69, which serves to retard the movement of the slide B1. Thus, the contact 6| in response to changes in the temperature of the related temperature zone,

.changes its position along the slide wire 60 and unbalances the resistance bridge, providing an electriclfnpulse whichactuates the controller 28 and changes the` fuel supply to the furnace in the manner 'described above.

Althoughthe movementof the contact 6| is tranismitted1trnndlately to the slide 61 through the springs 08, the action ofv the dash pot 69 retards the movement of the slide 61 so that it moves in the sameA direction as the contact It Will be evident that when the slide 61 has moved the same distance as the contact 6| in the same direction, the

bridge Will be restored toV itsnormal balanced `cations are within the scope of`tlie`present invention.'

Itv will be understood from the foregoing that the invention provides an improved apparatus for controlling temperatures within very close limits.' In the embodiments shown, for example, a change of the furnace temperature is noted almost as soon as it occurs, and the fuel supply adjusted before any change in the control temperature takes place. It thus provides an improved apparatus for detecting potential disturbances in the control temperature'and initiating regulatory action before the changes occur,

resulting in improved operation in those processes in which it may be used.

It is evident that the'invention may be used in other processes than the control of the tubular oil still described above, and it is to be understood that all such uses vare considered as being within the scope of the present invention. While a specific embodiment has been described above,

it is susceptible of numerous changes in form `and detailwithin the scope of the present invention and the latter is not intended in any way to be limited thereby, except as defined in the following claims.

1. In a system in which' changes in a control temperature are tobe regulated by temperature changes in a related temperature zone where heat is introduced into the systema pyrometric circuit comprising means responsive to the control temperature for impressing an E. .M. F. on said circuit, means disposed Ain'said related temperature Zone and responsive to the rate of change of temperature therein for Vadding a second E. M. F. to the said rst E. M. F., and means responsive to the resultant E. M. F.`in said circuit.

2. In a system in which changes in a control temperature are to be regulated by temperature changes in a related temperature zone where `heat is introduced into the system, a-tempera ture control device comprising electrical means responsive to the control temperature, electrical means disposed in said related temperature zone and responsive to the rate of change of temperature therein, both saidelectrcal means being connectedin series to provide a resultant electromotive force, means to adjust the hert supplied to the said related temperature zone, and means responsive to the said electromotive force for actuating the said heat adjusting neans to maintain the control temperature at a constant value.

3. In a system in which changes in a control temperature are to be regulated by temperature changes in a related temperature Zone where heat is introduced into the system, a temperature control device comprising a thermocouple having a hot junction responsive to thc'control temperature, a second thermocouple having at least-two hot junctions disposed in said related temperaturey 'zone and responsive to the temperature therein, and means for lagging one of said hot i junctions to/produce a time lag in response bcvtween the two said hot junctions, both said couples being .connected in series to provide an electro-v rnotive force which is a functionfof the control heat is introduced into the system, a temperature control device comprising electrical means responsive to the control temperature, `electri- A cal means disposed in said related temperature temperature, and the rate of change of tempera- Y ture in the'related temperature zone.

4. In a system in which changes in a control temperature are 'to be controlled by temperature changes in a related temperature zone where heat is introduced into the system, a temperature v control device comprising a thermocouple having a hot junction responsive to the control temperature, va secondther'mocouple having at least two hot junctions 'disposed in said related temperature zone and responsive to the temperature therein, and means for lagging one of said hot junctions to produce atime Vlag in response between the two said hot junctions substantially y equal in magnitude to the timelag between the control temperatureand the temperature of the related temperaturezone, both said couples being vconnected, in series to provide an electromotive force which is a function of the control temperature, and the rate of change of temperature in l the related temperature zone. f f

5. In a system in which changes in a control :EL

temperature are to be regulated by temperature changes ina related' temperature zone where heatis introduced into the system, a temperature control device comprising a pair yof series connected thermocouples, one of said couples :f

having a hot junction responsive to the control temperature, the other of said couples having twowires of similar metal connected to a third wire of different metal forming two hot junctions disposed in said related temperature Zone and responsive Ato, the temperature therein, means for lagging one of said last named hot junctions to providev a lag in response between the said junctions, whereby the total electromotive force of the series connected couples will be a function "of the control temperature, and the rate 0i" change of temperature of the related tempera- 'ture zone. f j

6. In a'system in which changes ina control I 'I temperature are to,V be regulated by temperature changes in a related temperature zone where'heat is introduced into the system, a temperature control device comprising three series vconnected `thermocouples, one'of said couples having a hot junction responsive tol the control temperature. the other two couples each having a hot junction disposed in said related tem- .perature zone and responsive to the temperature therein, andbcing oppostely connected so that their electromotive forces are opposed, and r"means for lagging the hot junction of one of ythe said last named couples to produce a time lag in response between it and said other couple, the electromotive force of thelagged couple being oppositely directed to the electromotive'force of the control temperature couple, whereby the total electromotive force of the series connected couples is a' function of the control temperature,

rand the rate of change of temperature in the related temperature zone.

zone and responsive to the rate of. change of temperature therein, both -said electrical means being connected in series to provide an electrornotiveforce which is a function of the control temperature, andthe rate of change of temperature in the related temperature zone, and means for amplifying the response of the said rate of change means.

' 8. Ina systemin which changes ina control temperature are to beiregulated by temperature changes in a related temperature zoner Where heat is introduced into the system, atemperaturecontrol device comprising a thermocouple` having a hot junction responsive'toith'e control temperature, a plurality of thermocouples 7. In a system in which changes 111,'acontrol ftemperature are to be'regulated bytemperature y changes in a related temperature zone where Vveach having two hot junctions disposed in said'f related temperature zone and responsive to the temperature therein, one of saidjunctions in each couple being lagged to provide a lag in response between Lthe two junctions of each couple, all of said couples being connected in series to provide a resultant electromotive force which is a function of the control temperature, and the rate of change of temperatnre in the Y related temperature zone.

9. In a system in which changes` in Va control y temperature are to be regulated by temperature changes in a related temperatureV zone, a temperature control device comprising a resistance bridge, a source of voltage' kfor the said bridge, a thermocouple having a hot junction@ responsive to thel control temperature, the said thermocouple being connected in a circuit across one diagonal of the bridge, and means respon-- sive to the vrate of f change of temperature inv the related temperaturezone for unbalancing f vthe bridge to provide a resultant electromotive 4force in said circuit which is a function of theV -control temperature, and the rate of change of temperature in the related temperature zone.

10. In a`systemin which changes in a control temperature are to be regulated by temperature changes in ,a 'related temperature zone, a temperature control device comprising a resistance bridge, asource of voltage for the said bridge,a thermocouple having a hot junction e responsive to the control temperaturepthe said.

thermocouple being connected in a circuit across one diagonal of the bridgeymeans for unbalancing the bridge, a controller `for thesaid unbalancing means, a thermocouple having a hot junction responsive to the temperature of the related temperature zone for actuating the said controller, means for restoring the bridgetoA balance, and meansfor retarding the v(said bal- .ancer restoring means, whereby the resultant electromotive force in said circuit is afunction of the, control temperature, and the rate of rchange of temperature in the related temperature zone.

y LUIS DE FLOREZ;

` EMMON BACH. 

